The 2011 ASHS Annual Conference

In order to obtain the expected benefits of a cover crop, the cover crop must grow vigorously. One of the main determinants of growth rate is planting date. We determined the appropriate planting dates for three summer cover crops for use on organic vegetable farms in the Great Lakes region. We measured how quickly soil was covered and the ability to compete with weed seedlings, as well as biomass production during the available growing period in trials on Certified Organic Land in three states across the region.  Spring-sown mustard (cvs ‘Tilney’ and ‘IdaGold’) performed well starting with seedings as soon as the ground can be worked (as early as March 15 in central Illinois, March 31 in central Michigan and April 5 in central New York). The latest date for successful spring establishment of mustards was May 1 in Illinois and May 15 in New York and Michigan, with reduced biomass production and minimal weed suppression for later-May plantings. Central Illinois is warmer, more fertile and has less flea beetle pressure, allowing planting as late as May 1 without significant weed competition or inadequate biomass. For late summer plantings, buckwheat required 600 GDD50 from planting to frost or mowing to produce sufficient growth and weed suppression.  In central NY, this corresponds to a cutoff date of mid-August. Sudangrass required 750 GDD50, with a cutoff in early August. Mustard could be sown until late August, requiring 1700 GDD32. These cover crops suppressed warm-season weeds (pigweed and lambsquarters) until low fall temperatures inhibited the cover crops, but cool season weeds (such as chickweed and shepherds purse) continued to grow after these cover crops were terminated by frost. A variety of environmental factors determined the extreme planting dates for these cover crops, but these limits can now be estimated for the whole region. Ample opportunities exist for establishing before or after vegetable crops. 

This research was supported by a grant from the USDA-NIFA Organic Research and Extension Initiative.